Losing the ability to smell (anosmia) or having a reduced sense of smell (hyposmia) is a common and often sudden symptom of a COVID-19 infection. This loss differs from the temporary congestion-related smell loss associated with a common cold because it frequently occurs even when nasal passages are clear. The inability to detect odors significantly impacts daily life, affecting safety by preventing the detection of hazards like smoke or spoiled food, and diminishing the enjoyment of eating. Understanding the typical recovery path is crucial for managing this experience.
The Range of Recovery Timelines
The majority of people who experience smell loss due to COVID-19 see a rapid return of their sense of smell. Research indicates that approximately 90% of affected individuals experience substantial recovery within the first four weeks following the onset of symptoms. The median recovery time for those who regain their sense of smell quickly is often reported to be around 11.5 days.
However, a portion of patients experience a more persistent form of olfactory dysfunction that extends well beyond this initial period. Studies following patients long-term have found that 81% of people recover their function within six months, but a small percentage, around 10% to 15%, may still have some degree of impairment a year or more after infection.
The loss occurs because the virus targets and damages the supporting cells, known as sustentacular cells, in the olfactory epithelium, rather than directly infecting the olfactory nerve cells. These supporting cells are necessary for the function and health of the sensory neurons responsible for detecting odors. Because the nerve cells are not the primary target, they can regenerate, which explains why most people recover quickly. Factors that may influence the duration of recovery include younger age, less severe initial disease, and the specific COVID-19 variant involved.
Understanding Smell Distortions
As the olfactory system attempts to repair and rewire itself, recovery is not always a smooth, linear process. Many patients experience smell distortions, which can be a temporary, yet frustrating, sign of the nerves attempting to reconnect correctly. The most common distortion is parosmia, which causes familiar odors to smell warped, unpleasant, or even disgusting.
Common triggers for parosmia include items like coffee, onions, garlic, and meat, which can suddenly smell like burning rubber, chemicals, or sewage. This phenomenon is thought to happen when the newly regenerating olfactory neurons are making faulty connections back to the brain’s processing centers. Another distortion is phantosmia, where a person perceives smells that are not actually present in the environment. While unsettling, the appearance of parosmia or phantosmia suggests that the underlying olfactory nerves are active and engaged in the regenerative process.
Strategies for Smell Training
Olfactory training is the most widely recommended intervention to restore the sense of smell after a viral infection. This simple, non-invasive process leverages neuroplasticity to encourage the brain and olfactory nerves to recalibrate their connections. The goal is to stimulate and reorganize the damaged olfactory pathways through repeated, mindful exposure to a small set of distinct scents.
The standard protocol involves using four different categories of scent. The training should be performed twice a day for a minimum duration of 12 weeks, though specialists recommend continuing for longer periods.
Scent Categories for Training
- Floral (e.g., rose)
- Resinous (e.g., eucalyptus)
- Fruity (e.g., lemon)
- Spicy (e.g., clove)
During each session, the person sniffs each of the four scents for about 20 seconds, concentrating and actively recalling how the odor used to smell. This mindful practice of associating the physical stimulus with the memory of the correct scent is a form of sensory “physical therapy.” Consistency and adherence to the twice-daily routine are associated with better outcomes for patients experiencing persistent smell loss.
When to Seek Specialized Care
While most cases of post-COVID smell loss resolve spontaneously or improve with smell training, specific markers suggest it is time to consult a specialist. If there has been no noticeable improvement in smell function after two to three months, seeking an evaluation from an otolaryngologist (ENT doctor) is advisable. This timeframe allows for the initial period of natural recovery to pass and for a course of at-home smell training to begin showing effect.
A specialist can objectively measure the extent of the smell deficit using standardized tests and rule out other non-COVID-related causes of persistent smell loss. Conditions such as nasal polyps, chronic sinusitis, or other neurological issues can also cause anosmia and require different treatment approaches. In cases of persistent loss, a specialist may discuss advanced options, including topical steroid rinses or other emerging treatments.